The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Research Report: Human LONP2 (UniProt Q86WA8) — Functional Annotation and Current Evidence

1. Target verification (identity, organism, and domain agreement)

The research target LONP2 (Homo sapiens) corresponds to a peroxisomal Lon protease (Lon protease homolog 2), distinct from the mitochondrial paralog LONP1. Authoritative synthesis of the field describes human LonP2 as a nuclear-encoded ~852 aa (~95 kDa) LonA-family protease, with the canonical Lon architecture: an N-terminal substrate-recognition region, an AAA+ ATPase domain (Walker motifs), and a C-terminal serine protease domain with a catalytic Ser–Lys dyad; the protein is peroxisome-targeted by a C-terminal PTS1 motif (reported as SRL in humans). (pomatto2017theperoxisomallon pages 4-6)

2. Key concepts and definitions (current understanding)

2.1 What kind of enzyme is LONP2?

LONP2 is an ATP-dependent Lon-family serine protease (LonA-type), annotated as EC 3.4.21.53, meaning it is an endopeptidase using an active-site serine for catalysis and requiring ATP hydrolysis (via its AAA+ module) to unfold and process substrates. Lon-family proteases are frequently described as protease/chaperone systems: ATP binding/hydrolysis supports substrate recognition, unfolding, and proteolytic turnover of damaged or misfolded proteins. (pomatto2017theperoxisomallon pages 4-6, yamashita2023depletionoflonp2 pages 1-2)

2.2 Peroxisomal protein quality control (PQC)

Peroxisomes import many matrix proteins post-translationally and must remove damaged or dysfunctional proteins to preserve organelle function. A 2023 review of peroxisomal import and quality control emphasizes that most organisms harbor a peroxisomal LON protease to degrade misfolded/dysfunctional peroxisomal matrix proteins, while peroxisomal membrane protein QC relies heavily on the ubiquitin–proteasome system (UPS) and extraction machineries. (rudowitz2023importandquality pages 7-8)

3. Subcellular localization and import mechanism

3.1 Localization: peroxisomal matrix (core enrichment reported in liver)

LonP2 was originally identified as a peroxisome-specific Lon isoform and localized to peroxisomes in mammalian tissues; expert synthesis reports that it can concentrate in the dense core of rat liver peroxisomes, a highly oxidizing microenvironment. (pomatto2017theperoxisomallon pages 3-4)

3.2 Import signal: C-terminal PTS1

LonP2 is targeted to the peroxisomal matrix via a C-terminal PTS1 motif (reported as SRL in human LonP2), consistent with peroxisomal matrix import pathways. (pomatto2017theperoxisomallon pages 4-6)

3.3 Recent functional readout of matrix import failure upon LONP2 depletion (2023)

In mammalian cells, LONP2 silencing causes failure of matrix import for a canonical luminal reporter (CFP-SKL, a PTS1-containing protein), while import of a membrane marker (PEX3-YFP) is maintained, consistent with selective impairment of matrix/lumenal proteostasis and/or import competency rather than generalized peroxisome biogenesis collapse. (yamashita2023depletionoflonp2 pages 2-5)

Figure-based evidence from the 2023 Biology Direct study visually shows diffuse CFP-SKL (loss of punctate peroxisomal localization) after LONP2 knockdown, and quantifies associated peroxisome morphological changes. (yamashita2023depletionoflonp2 media 013dcd11)

4. Primary molecular function: enzymatic activity and substrate specificity

4.1 Biochemical activity (ATP-stimulated proteolysis)

Authoritative review of biochemical work indicates purified LonP2 is an ATPase and an ATP-stimulated protease: it degrades model misfolded substrates such as α- and β-casein in vitro only in the presence of ATP, and catalytic-serine mutation abolishes proteolysis. This supports a classical Lon mechanism coupling AAA+ ATPase activity to proteolysis. (pomatto2017theperoxisomallon pages 4-6)

4.2 Substrate classes and specificity (oxidation/misfolding; pathway-linked substrates)

Current evidence supports two major substrate categories:

1. Oxidatively damaged/misfolded peroxisomal proteins. Expert synthesis describes LonP2 as important in clearing oxidatively damaged proteins generated in the ROS-rich peroxisomal environment. Oxidation can convert otherwise resistant proteins into LonP2 substrates; one example discussed is that catalase becomes susceptible to LonP2-dependent degradation after oxidative pretreatment. (pomatto2017theperoxisomallon pages 7-8)

2. Regulatory protease TYSND1 (turnover of cleavage products). A key primary substrate relationship is that TYSND1 self-cleaves into smaller chains that are subsequently degraded by peroxisomal Lon protease (PsLon/LONP2). This positions LONP2 as a regulator of peroxisomal protease homeostasis and indirectly links it to maturation/processing of β-oxidation enzymes that are TYSND1 substrates. (okumoto2011twoproteasestrypsin pages 1-2, okumoto2011twoproteasestrypsin pages 2-3)

4.3 Impact on peroxisomal fatty-acid β-oxidation (functional coupling)

In a primary study of peroxisomal proteases, knockdown of TYSND1 significantly reduced peroxisomal β-oxidation of a very-long-chain fatty acid, and knockdown of PsLon/LONP2 partially lowered β-oxidation, consistent with a modulatory role for LONP2 in maintaining the peroxisomal enzyme environment required for efficient β-oxidation. The assay used 1-14C-labeled lignoceric acid in HeLa cells and quantified acid-soluble products. (okumoto2011twoproteasestrypsin pages 3-4, okumoto2011twoproteasestrypsin pages 1-2)

5. Biological roles and pathways (mechanistic interpretation)

5.1 LONP2 as a peroxisomal proteostasis “protease/chaperone”

A 2023 primary study frames LONP2 as a peroxisomal protease/chaperone and demonstrates that acute LONP2 silencing triggers “early” peroxisomal proteotoxic stress: accumulation of the reported substrate TYSND1 occurs while some downstream TYSND1-dependent processing (e.g., ACOX1 processing) appears initially preserved, suggesting LONP2 loss first perturbs matrix proteostasis and organelle competence before large-scale loss of peroxisomal proteins. (yamashita2023depletionoflonp2 pages 1-2, yamashita2023depletionoflonp2 pages 2-5)

5.2 Peroxisome morphology, number, and matrix import competency

Upon LONP2 depletion, peroxisomes become fewer and enlarged/elongated, and matrix import fails for a luminal reporter, establishing LONP2 as a determinant of peroxisome structural/functional homeostasis. (yamashita2023depletionoflonp2 pages 2-5, yamashita2023depletionoflonp2 media 013dcd11)

5.3 Cell-type-specific stress signaling and lipid/cholesterol remodeling (2023)

Acute LONP2 silencing reveals organelle-to-cell signaling outputs:
- In COS-7 cells, LONP2 depletion strongly activates the integrated stress response (ISR), with induction of associated stress programs. (yamashita2023depletionoflonp2 pages 1-2)
- In both COS-7 and U2OS cells, common responses include repression of retinoic acid signaling, increased sphingolipids, and cholesterol accumulation in endomembrane compartments, consistent with peroxisome contributions to cholesterol flux out of late endosomes. (yamashita2023depletionoflonp2 pages 1-2)

The associated lipidomics dataset reported 2,094 lipid features detected and 206 annotated (n=5 independent experiments), grounding these pathway links in broad quantitative lipid remodeling. (yamashita2023depletionoflonp2 pages 9-11)

5.4 Relationship to pexophagy and peroxisome quality-control circuits

Peroxisome QC can engage autophagic turnover (pexophagy) when import is impaired or peroxisomes are damaged. Mechanistic context highlights sentinel roles of peroxisome import machinery (e.g., PEX2-mediated ubiquitination recruiting p62/NBR1) in targeting peroxisomes for pexophagy when import is compromised; LONP2 depletion is proposed as a useful perturbation to probe how matrix proteotoxicity couples to import stress and turnover pathways. (yamashita2023elucidatingmechanismof pages 27-33)

Notably, in the 2023 LONP2 knockdown experiments, there was no evidence of induced pexophagy under the tested conditions (no increase in LC3/p62 colocalization with peroxisomes), indicating that LONP2-dependent proteotoxic stress can manifest without necessarily triggering bulk pexophagy in the acute setting. (yamashita2023depletionoflonp2 pages 2-5)

6. Recent developments (prioritizing 2023–2024)

6.1 2023: Import and quality control review updates

A 2023 Journal of Cell Science review synthesizes updated models of peroxisomal protein import and QC and reiterates that peroxisomal matrix protein QC commonly depends on a peroxisomal LON protease, placing LONP2 within a conserved QC module across eukaryotes. (rudowitz2023importandquality pages 7-8)

6.2 2023: New experimental evidence linking LONP2 to cholesterol trafficking and RA signaling

The 2023 Biology Direct study provides a direct experimental perturbation of LONP2 showing connections to cholesterol trafficking defects (cholesterol trapped in endomembranes) and repression of retinoic acid signaling, suggesting that peroxisomal proteostasis can influence broader lipid signaling programs and sterol flux. (yamashita2023depletionoflonp2 pages 1-2, yamashita2023depletionoflonp2 pages 9-11)

6.3 2023: Community/expert synthesis emphasizes variable cellular responses and cholesterol phenotypes

A 2023 peroxisome meeting report highlights that LONP2 silencing yields ubiquitous peroxisomal phenotypes across cell types but with variable magnitude of global cellular stress responses, and it emphasizes blocked cholesterol flux between lysosomes and ER with lysosomal cholesteryl ester accumulation. (pedrosa2023peroxisomesnovel pages 7-8)

6.4 2024: Peroxisome homeostasis/turnover mechanisms continue to be mapped

A 2024 Nature Communications study on basal pexophagy and peroxisome membrane protein turnover places peroxisomal matrix QC components (including PsLon/LONP2 and TYSND1) within the broader network maintaining peroxisomal integrity, reinforcing that peroxisome homeostasis integrates matrix proteostasis with membrane-protein turnover and autophagy regulation. (OpenTargets Search: -LONP2)

7. Current applications and real-world implementations

7.1 Experimental implementation as a peroxisomal proteotoxic-stress model

LONP2 depletion has emerged as an experimentally tractable means to induce peroxisomal proteotoxic stress and study downstream consequences, including matrix import defects, peroxisome remodeling, ISR engagement (cell-type dependent), and cholesterol trafficking abnormalities. This provides a functional model system for dissecting peroxisome–endomembrane communication and stress signaling. (yamashita2023depletionoflonp2 pages 1-2, yamashita2023depletionoflonp2 pages 2-5, yamashita2023depletionoflonp2 media 013dcd11)

7.2 Disease association resources (database-driven; caution on causality)

Open Targets lists disease associations for LONP2 (ENSG00000102910), including terms such as Buratti–Harel syndrome, neurodevelopmental disorder, gestational diabetes, neurodegenerative disease, and esophageal disease, with linked literature evidence (e.g., PMID 32430360). These should be treated as association evidence rather than definitive mechanistic proof of causality for LONP2, pending focused experimental/clinical studies. (OpenTargets Search: -LONP2)

8. Expert opinion and analysis (authoritative perspectives)

A domain-leading review emphasizes that, relative to LONP1, LonP2/LONP2 remains less well characterized in mechanistic and clinical terms, despite strong evidence for a core role in peroxisomal proteostasis. It highlights multiple open questions: how LonP2 selects substrates in vivo, how ATP hydrolysis is coupled to unfolding/proteolysis in peroxisomes, and how LonP2-mediated proteostasis intersects with organelle turnover pathways and organismal aging/disease. (pomatto2017theperoxisomallon pages 1-2, pomatto2017theperoxisomallon pages 4-6)

9. Quantitative highlights from recent and foundational studies

• Peroxisome morphology/import (2023): LONP2 knockdown decreases peroxisome number and increases peroxisome size, while causing loss of punctate peroxisomal localization of a CFP-SKL luminal reporter (quantified and imaged in Fig. 1). (yamashita2023depletionoflonp2 media 013dcd11)
• Lipidomics scale (2023): 2,094 lipid features detected and 206 annotated in the LONP2 depletion study (n=5). (yamashita2023depletionoflonp2 pages 9-11)
• Cholesterol phenotype rescue timing (2023): cholesterol clearance phenotype was reported to be rescued after 48 h of transient expression of siRNA-resistant LONP2 cDNA. (yamashita2023depletionoflonp2 pages 9-11)
• ROS context (reviewed values): peroxisomal H2O2 production rates were summarized as ~44–172 nmol·min−1·g−1 protein, with ~30% diffusion to cytosol (~13.2–51.6 nmol·min−1·g−1 protein); and 100 μM H2O2 was reported to cause ~40% loss of catalase function (context for oxidative substrate generation relevant to LonP2 substrate selection). (pomatto2017theperoxisomallon pages 7-8)

10. Consolidated evidence map

The following table summarizes the strongest evidence-supported claims about LONP2/Q86WA8 across identity, localization, enzymatic function, substrates, pathway roles, and disease association context.

Table: This table condenses the strongest gathered evidence on human LONP2/Q86WA8, covering verified identity, localization, enzymatic function, substrates, pathway roles, and disease evidence. It is designed as a citation-ready scaffold for the final research report.

11. Key references (with publication dates and URLs)

• Yamashita A. et al. (2023-09). Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism. Biology Direct. https://doi.org/10.1186/s13062-023-00416-3 (yamashita2023depletionoflonp2 pages 1-2, yamashita2023depletionoflonp2 pages 2-5, yamashita2023depletionoflonp2 pages 9-11, yamashita2023depletionoflonp2 media 013dcd11)
• Rudowitz M, Erdmann R. (2023-08). Import and quality control of peroxisomal proteins. Journal of Cell Science. https://doi.org/10.1242/jcs.260999 (rudowitz2023importandquality pages 7-8)
• Pedrosa AG. et al. (2023-05). Peroxisomes: novel findings and future directions. Histochemistry and Cell Biology. https://doi.org/10.1007/s00418-023-02201-9 (pedrosa2023peroxisomesnovel pages 7-8)
• Okumoto K, Kametani Y, Fujiki Y. (2011-12). Two Proteases, Tysnd1 and Peroxisomal Lon Protease (PsLon), Cooperatively Regulate Fatty Acid β-Oxidation in Peroxisomal Matrix. J Biol Chem. https://doi.org/10.1074/jbc.m111.285197 (okumoto2011twoproteasestrypsin pages 1-2, okumoto2011twoproteasestrypsin pages 2-3)
• Pomatto LCD, Raynes R, Davies KJA. (2017-05). The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1. Biological Reviews. https://doi.org/10.1111/brv.12253 (pomatto2017theperoxisomallon pages 4-6)
• Open Targets Platform (accessed via tool context). LONP2 disease associations (evidence linked to PMID 32430360). https://platform.opentargets.org/target/ENSG00000102910 (OpenTargets Search: -LONP2)

References

1. (pomatto2017theperoxisomallon pages 4-6): Laura C. D. Pomatto, Rachel Raynes, and Kelvin J. A. Davies. The peroxisomal lon protease lonp2 in aging and disease: functions and comparisons with mitochondrial lon protease lonp1. Biological Reviews, 92:739-753, May 2017. URL: https://doi.org/10.1111/brv.12253, doi:10.1111/brv.12253. This article has 56 citations and is from a domain leading peer-reviewed journal.

2. (yamashita2023depletionoflonp2 pages 1-2): Akihiro Yamashita, Olesia Ignatenko, Mai Nguyen, Raphaëlle Lambert, Kathleen Watt, Caroline Daneault, Isabelle Robillard-Frayne, Ivan Topisirovic, Christine Des Rosiers, and Heidi M. McBride. Depletion of lonp2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism. Biology Direct, Sep 2023. URL: https://doi.org/10.1186/s13062-023-00416-3, doi:10.1186/s13062-023-00416-3. This article has 3 citations and is from a peer-reviewed journal.

3. (rudowitz2023importandquality pages 7-8): Markus Rudowitz and Ralf Erdmann. Import and quality control of peroxisomal proteins. Journal of cell science, Aug 2023. URL: https://doi.org/10.1242/jcs.260999, doi:10.1242/jcs.260999. This article has 21 citations and is from a domain leading peer-reviewed journal.

4. (pomatto2017theperoxisomallon pages 3-4): Laura C. D. Pomatto, Rachel Raynes, and Kelvin J. A. Davies. The peroxisomal lon protease lonp2 in aging and disease: functions and comparisons with mitochondrial lon protease lonp1. Biological Reviews, 92:739-753, May 2017. URL: https://doi.org/10.1111/brv.12253, doi:10.1111/brv.12253. This article has 56 citations and is from a domain leading peer-reviewed journal.

5. (yamashita2023depletionoflonp2 pages 2-5): Akihiro Yamashita, Olesia Ignatenko, Mai Nguyen, Raphaëlle Lambert, Kathleen Watt, Caroline Daneault, Isabelle Robillard-Frayne, Ivan Topisirovic, Christine Des Rosiers, and Heidi M. McBride. Depletion of lonp2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism. Biology Direct, Sep 2023. URL: https://doi.org/10.1186/s13062-023-00416-3, doi:10.1186/s13062-023-00416-3. This article has 3 citations and is from a peer-reviewed journal.

6. (yamashita2023depletionoflonp2 media 013dcd11): Akihiro Yamashita, Olesia Ignatenko, Mai Nguyen, Raphaëlle Lambert, Kathleen Watt, Caroline Daneault, Isabelle Robillard-Frayne, Ivan Topisirovic, Christine Des Rosiers, and Heidi M. McBride. Depletion of lonp2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism. Biology Direct, Sep 2023. URL: https://doi.org/10.1186/s13062-023-00416-3, doi:10.1186/s13062-023-00416-3. This article has 3 citations and is from a peer-reviewed journal.

7. (pomatto2017theperoxisomallon pages 7-8): Laura C. D. Pomatto, Rachel Raynes, and Kelvin J. A. Davies. The peroxisomal lon protease lonp2 in aging and disease: functions and comparisons with mitochondrial lon protease lonp1. Biological Reviews, 92:739-753, May 2017. URL: https://doi.org/10.1111/brv.12253, doi:10.1111/brv.12253. This article has 56 citations and is from a domain leading peer-reviewed journal.

8. (okumoto2011twoproteasestrypsin pages 1-2): Kanji Okumoto, Yukari Kametani, and Yukio Fujiki. Two proteases, trypsin domain-containing 1 (tysnd1) and peroxisomal lon protease (pslon), cooperatively regulate fatty acid β-oxidation in peroxisomal matrix. Journal of Biological Chemistry, 286:44367-44379, Dec 2011. URL: https://doi.org/10.1074/jbc.m111.285197, doi:10.1074/jbc.m111.285197. This article has 67 citations and is from a domain leading peer-reviewed journal.

9. (okumoto2011twoproteasestrypsin pages 2-3): Kanji Okumoto, Yukari Kametani, and Yukio Fujiki. Two proteases, trypsin domain-containing 1 (tysnd1) and peroxisomal lon protease (pslon), cooperatively regulate fatty acid β-oxidation in peroxisomal matrix. Journal of Biological Chemistry, 286:44367-44379, Dec 2011. URL: https://doi.org/10.1074/jbc.m111.285197, doi:10.1074/jbc.m111.285197. This article has 67 citations and is from a domain leading peer-reviewed journal.

10. (okumoto2011twoproteasestrypsin pages 3-4): Kanji Okumoto, Yukari Kametani, and Yukio Fujiki. Two proteases, trypsin domain-containing 1 (tysnd1) and peroxisomal lon protease (pslon), cooperatively regulate fatty acid β-oxidation in peroxisomal matrix. Journal of Biological Chemistry, 286:44367-44379, Dec 2011. URL: https://doi.org/10.1074/jbc.m111.285197, doi:10.1074/jbc.m111.285197. This article has 67 citations and is from a domain leading peer-reviewed journal.

11. (yamashita2023depletionoflonp2 pages 9-11): Akihiro Yamashita, Olesia Ignatenko, Mai Nguyen, Raphaëlle Lambert, Kathleen Watt, Caroline Daneault, Isabelle Robillard-Frayne, Ivan Topisirovic, Christine Des Rosiers, and Heidi M. McBride. Depletion of lonp2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism. Biology Direct, Sep 2023. URL: https://doi.org/10.1186/s13062-023-00416-3, doi:10.1186/s13062-023-00416-3. This article has 3 citations and is from a peer-reviewed journal.

12. (yamashita2023elucidatingmechanismof pages 27-33): A Yamashita. Elucidating mechanism of peroxisomal homeostasis in mammalian cells. Unknown journal, 2023.

13. (pedrosa2023peroxisomesnovel pages 7-8): Ana G. Pedrosa, Katharina Reglinski, Celien Lismont, Suzan Kors, Joseph Costello, Tony A. Rodrigues, Mariana Marques, Nicole Linka, Catherine Argyriou, Isabelle Weinhofer, Sai Kocherlakota, Victoria Riccio, Vanessa Ferreira, Francesca Di Cara, Ana Rita Ferreira, Tânia Francisco, Jorge E. Azevedo, and Daniela Ribeiro. Peroxisomes : novel findings and future directions. Histochemistry and Cell Biology, 159:379-387, May 2023. URL: https://doi.org/10.1007/s00418-023-02201-9, doi:10.1007/s00418-023-02201-9. This article has 3 citations and is from a peer-reviewed journal.

14. (OpenTargets Search: -LONP2): Open Targets Query (-LONP2, 5 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.

15. (pomatto2017theperoxisomallon pages 1-2): Laura C. D. Pomatto, Rachel Raynes, and Kelvin J. A. Davies. The peroxisomal lon protease lonp2 in aging and disease: functions and comparisons with mitochondrial lon protease lonp1. Biological Reviews, 92:739-753, May 2017. URL: https://doi.org/10.1111/brv.12253, doi:10.1111/brv.12253. This article has 56 citations and is from a domain leading peer-reviewed journal.

16. (okumoto2011twoproteasestrypsin pages 4-5): Kanji Okumoto, Yukari Kametani, and Yukio Fujiki. Two proteases, trypsin domain-containing 1 (tysnd1) and peroxisomal lon protease (pslon), cooperatively regulate fatty acid β-oxidation in peroxisomal matrix. Journal of Biological Chemistry, 286:44367-44379, Dec 2011. URL: https://doi.org/10.1074/jbc.m111.285197, doi:10.1074/jbc.m111.285197. This article has 67 citations and is from a domain leading peer-reviewed journal.

Artifacts

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Citations

1. pomatto2017theperoxisomallon pages 4-6
2. rudowitz2023importandquality pages 7-8
3. pomatto2017theperoxisomallon pages 3-4
4. pomatto2017theperoxisomallon pages 7-8
5. yamashita2023elucidatingmechanismof pages 27-33
6. pedrosa2023peroxisomesnovel pages 7-8
7. okumoto2011twoproteasestrypsin pages 1-2
8. okumoto2011twoproteasestrypsin pages 2-3
9. okumoto2011twoproteasestrypsin pages 3-4
10. pomatto2017theperoxisomallon pages 1-2
11. okumoto2011twoproteasestrypsin pages 4-5
12. https://doi.org/10.1111/brv.12253
13. https://doi.org/10.1186/s13062-023-00416-3
14. https://doi.org/10.1074/jbc.m111.285197
15. https://doi.org/10.1242/jcs.260999
16. https://doi.org/10.1007/s00418-023-02201-9
17. https://platform.opentargets.org/target/ENSG00000102910
18. https://doi.org/10.1111/brv.12253,
19. https://doi.org/10.1186/s13062-023-00416-3,
20. https://doi.org/10.1242/jcs.260999,
21. https://doi.org/10.1074/jbc.m111.285197,
22. https://doi.org/10.1007/s00418-023-02201-9,

LONP2 (Lon Peptidase 2, Peroxisomal) – Function, Processes, and Localization

Gene and Protein Overview

LONP2 encodes the human peroxisomal Lon protease, an ATP-dependent protease of the Lon family that localizes to the peroxisome matrix (www.ncbi.nlm.nih.gov). It is a paralog of the mitochondrial Lon protease (LONP1), arising from an early gene duplication retained from bacterial ancestors (biologydirect.biomedcentral.com). LONP2 is a AAA⁺ serine protease composed of distinct domains: an N-terminal “Lon N” domain for substrate recognition, a central ATPase (AAA⁺) domain that harnesses ATP hydrolysis, and a C-terminal peptidase domain containing the catalytic serine (www.ncbi.nlm.nih.gov). In its longer isoforms, LONP2 carries a peroxisome targeting signal type 1 (PTS1) tripeptide at the extreme C-terminus, ensuring import into the peroxisomal lumen (www.ncbi.nlm.nih.gov). Like other Lon proteases, LONP2 assembles into a multimeric ring (heptameric in fungi) which unfolds and translocates substrate polypeptides into its proteolytic core (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This protein is expressed in most human tissues (notably high in metabolically active organs like liver and thyroid) consistent with the ubiquitous presence of peroxisomes (www.ncbi.nlm.nih.gov).

Enzymatic Function and Substrate Specificity

LONP2’s primary function is quality-control proteolysis: it selectively recognizes and degrades misfolded, damaged, or unassembled proteins within the peroxisomal matrix (www.genecards.org) (pmc.ncbi.nlm.nih.gov). Biochemically, it is an ATP-dependent serine protease, meaning ATP binding/hydrolysis is required for efficient protein degradation and a serine residue acts in its catalytic center. Experimental studies have demonstrated this mechanism directly – isolated peroxisomal LONP2 can rapidly digest model unfolded substrates (like casein) only in the presence of ATP (pmc.ncbi.nlm.nih.gov). Mutating the enzyme’s active-site serine abolishes its proteolytic activity, confirming that catalysis depends on this residue (pmc.ncbi.nlm.nih.gov). Thus, LONP2 uses ATP to drive conformational changes and substrate unfolding (as seen with mitochondrial Lon), allowing it to thread substrates into the protease chamber for degradation (pmc.ncbi.nlm.nih.gov).

LONP2 is often described as “dual-function” – a protease and a chaperone (pmc.ncbi.nlm.nih.gov). In addition to outright degradation of polypeptides, it can bind and stabilize unfolded proteins to prevent aggregation, acting in a chaperone-like capacity (pmc.ncbi.nlm.nih.gov). This was shown in fungal models where LONP2 (called Pln in yeast) was able to refold or hold substrates in vitro, and its loss led to accumulation of insoluble protein aggregates in peroxisomes (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). These findings indicate LONP2 can either refold stressed proteins or commit them to degradation, thereby maintaining a healthy folding environment in the organelle.

Substrate specificity of LONP2 appears to target proteins that are abnormal or no longer functional. It does not generally destroy native, functional enzymes, but rather “selectively digests unfolded or oxidatively damaged proteins” (pmc.ncbi.nlm.nih.gov). A prime example is catalase: in fungi, oxidatively damaged catalase-peroxidase (a peroxisomal enzyme prone to oxidative inactivation) was shown to be a LONP2 substrate, whereas the native (undamaged) catalase was spared (pmc.ncbi.nlm.nih.gov). Cells lacking LONP2 accumulate high levels of catalase-peroxidase protein that is aggregated and enzymatically inactive (pmc.ncbi.nlm.nih.gov), demonstrating that LONP2 normally removes the oxidized forms to prevent such aggregation. Another well-characterized substrate is TYSND1, a peroxisomal matrix protease. TYSND1 (trypsin domain-containing protease 1) undergoes an auto-proteolysis to generate 45 kDa and 15 kDa fragments, and LONP2 recognizes and degrades these TYSND1 fragments (pmc.ncbi.nlm.nih.gov). This was shown in mammalian cells: when LONP2 is knocked down, the cleaved fragments of TYSND1 accumulate to high levels (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com). Notably, TYSND1 itself is responsible for processing several peroxisomal enzymes – it cleaves the C-terminal targeting tripeptides of some PTS1 enzymes and removes N-terminal leader peptides from PTS2 enzymes (such as the precursor of 3-ketoacyl-CoA thiolase) (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). LONP2 thus indirectly supports these maturation steps: by degrading TYSND1 after it acts, LONP2 may reset the protease for further use or prevent an excess of its cleaved form from interfering with peroxisomal protease balance (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). In line with this, LONP2 is considered necessary for efficient processing of PTS2-containing proteins and normal peroxisomal enzyme turnover (www.genecards.org). Beyond TYSND1 and catalase, LONP2 likely targets other misfolded or surplus peroxisomal matrix proteins (e.g. import adapters or metabolic enzymes) especially if they become oxidized. In yeast and plants, additional client proteins for LONP2 have been observed, reinforcing its broad role: for instance, studies in Penicillium and Hansenula yeast identified catalase and other matrix enzymes as LONP2-dependent degradation targets (biologydirect.biomedcentral.com).

Overall, LONP2 exhibits substrate specificity in favor of “non-native” polypeptides. By binding exposed hydrophobic segments or unstructured regions (hallmarks of damaged or misfolded proteins), it discriminates defective proteins from the normal folded pool (pmc.ncbi.nlm.nih.gov). This behavior is analogous to the selectivity of cytosolic proteostasis systems (like the ubiquitin-proteasome) for aberrant proteins, but LONP2 is the dedicated protease within peroxisomes where the ubiquitin-proteasome system is absent (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

Localization and Peroxisomal Context

LONP2 is strictly localized to peroxisomes – specifically, the matrix (lumen) of this organelle (pmc.ncbi.nlm.nih.gov). Newly synthesized LONP2 in the cytosol is recognized and imported into peroxisomes via the PTS1 pathway, thanks to its C-terminal import signal (www.ncbi.nlm.nih.gov). The imported protein oligomerizes into a cylindrical protease complex that resides in the peroxisomal matrix, presumably free in the lumen rather than membrane-bound (similar to mitochondrial LonP1). Within peroxisomes, LONP2 is strategically positioned in an environment of high oxidative risk. Peroxisomes carry out β-oxidation of very-long-chain fatty acids and other oxidative reactions that produce hydrogen peroxide (H₂O₂) and reactive oxygen species (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Indeed, the peroxisomal core is often a site of concentrated H₂O₂ (e.g. from urate oxidase in some species) (pmc.ncbi.nlm.nih.gov). Therefore, many peroxisomal enzymes (like fatty acid oxidases and catalase) face continual oxidative stress and potential damage. LONP2’s presence in the peroxisomal lumen provides an on-site defense, immediately recognizing and removing proteins that have been inactivated by oxidation (pmc.ncbi.nlm.nih.gov). This proximity is critical – as noted by Pomatto et al. (2017), it is “logical that a proteolytic enzyme such as LonP2 would be in close proximity [to vulnerable proteins] to prevent protein aggregation,” much as mitochondrial LonP1 sits in the mitochondrial matrix to degrade oxidized respiratory chain proteins (pmc.ncbi.nlm.nih.gov). Consistently, LONP2 is relatively abundant in the peroxisome compared to other matrix proteins, highlighting its importance in such a highly oxidizing compartment (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

The peroxisomal localization of LONP2 is also tied to its role in protein import and processing pathways. Peroxisomes import all their matrix enzymes post-translationally from the cytosol via PEX5/PTS1 or PEX7/PTS2 pathways (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Once inside, some newly imported proteins undergo proteolytic clipping (e.g. removal of PTS2 pre-sequences or C-terminal propeptides) to become fully active. LONP2 cooperates in this maturation process: for example, the PTS2-containing thiolase requires cleavage of its N-terminal presequence by TYSND1, and LONP2 then degrades the excised presequence and any excess TYSND1 fragments (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). By clearing such peptides and inactive intermediates, LONP2 helps maintain a proper proteostasis balance that facilitates ongoing import. In fact, recent evidence indicates that if LONP2 is suppressed, peroxisomal protein import can be impaired. A 2023 study by Bailey et al. showed that silencing LONP2 led to accumulation of peroxisomal protein fragments and a failure of new proteins to import into the peroxisome lumen (biologydirect.biomedcentral.com). In LONP2-deficient cells, a fluorescent PTS1 reporter (CFP–SKL) could no longer efficiently translocate into peroxisomes even though membrane proteins still inserted normally, indicating a specific defect in matrix import likely due to a clogged or hostile luminal environment (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com). This suggests that LONP2’s activity is required to “prepare the ground” for incoming proteins, perhaps by keeping the matrix clear of aggregates or by degrading improperly imported proteins that might otherwise tie up the import machinery.

Role in Peroxisomal Homeostasis and Metabolic Pathways

LONP2 is now recognized as a key protector of peroxisomal homeostasis. By continuously eliminating damaged proteins, LONP2 prevents the formation of protein aggregates that could disrupt organelle function (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). This role is especially crucial in the face of reactive oxygen species generated inside peroxisomes. Pomatto et al. note that Lon protease–mediated degradation of oxidized proteins is “a vital mechanism to maintain protein homeostasis within the peroxisome,” providing a critical defense against the accumulation of oxidative damage (pmc.ncbi.nlm.nih.gov). If LONP2 is lacking or overwhelmed, peroxisomes swiftly lose functional capacity. Experiments in yeast and fungi have dramatically illustrated this: deleting the peroxisomal Lon gene in yeast leads to elevated levels of ROS, protein aggregates inside peroxisomes, and even increased DNA damage in the cell (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov) (likely because unchecked peroxisomal oxidation by-products can damage nuclear or mitochondrial DNA). These Lon-deficient peroxisomes often become enlarged and increase in number – a probable compensation attempt by the cell to dilute or handle the proteostatic stress (pmc.ncbi.nlm.nih.gov). In Penicillium chrysogenum lacking Lon, researchers observed significantly enlarged peroxisomes filled with electron-dense inclusion bodies of aggregated proteins (mostly oxidized catalase) (pmc.ncbi.nlm.nih.gov). Those mutant cells also showed reduced peroxisomal enzyme activities, despite elevated protein levels, consistent with many enzymes being present in a non-functional, aggregated state (pmc.ncbi.nlm.nih.gov).

Coordination with pexophagy – the autophagic degradation of peroxisomes – is another important aspect of LONP2’s role. Under normal conditions, LONP2 handles routine cleanup of damaged proteins internally; however, if damage accumulates beyond a threshold, entire peroxisomes may be removed by selective autophagy. Studies in yeast underscore this relationship: loss of LONP2 alone has modest growth effects, but simultaneous loss of LONP2 and the key autophagy gene ATG1 is highly detrimental (pmc.ncbi.nlm.nih.gov). Aksam et al. (2007) showed that a double knockout of the peroxisomal Lon protease gene (pln) and atg1 in yeast led to synergistic lethality – cells could not survive without both the protease-based quality control and the backup autophagy system (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). In these double mutants, irreparable protein damage simply accumulates: peroxisomes grew larger and more numerous (unable to be turned over), and protein aggregates built up unchecked (pmc.ncbi.nlm.nih.gov). This indicates that LONP2 and pexophagy together constitute a two-tiered proteostasis system for peroxisomes (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). LONP2 handles the first line of defense, degrading individual damaged proteins as they arise, whereas pexophagy provides a rescue pathway if an entire organelle becomes too damaged to repair. Consistently, in cells with LONP2 knocked down, there are signs of peroxisomal stress but not immediate activation of autophagy: 6-day LONP2 silencing did not significantly induce pexophagy or general autophagy markers (biologydirect.biomedcentral.com), suggesting that peroxisomes remained intact and were not being rapidly cleared. Instead, the cell activates other stress responses (discussed below) while presumably attempting to cope or wait for longer-term solutions. If the stress were prolonged or acute enough, pexophagy would likely kick in. This cooperative interaction underlines LONP2’s importance – it delays or prevents the need for destructive solutions by continually rejuvenating peroxisomes at the protein level.

Importantly, LONP2’s activity has direct implications for metabolic pathways housed in peroxisomes, especially fatty acid β-oxidation. Peroxisomes are crucial for breaking down very-long-chain fatty acids (VLCFAs) and branched-chain lipids, which are then shuttled to mitochondria for completion of oxidation (biologydirect.biomedcentral.com). Many enzymes of the β-oxidation cycle reside in the peroxisomal matrix (e.g. acyl-CoA oxidase 1 – ACOX1, the D-bifunctional enzyme, thiolase). The proper turnover and maturation of these enzymes are partly governed by TYSND1 and LONP2. Evidence shows that disrupting LONP2 can hamper peroxisomal β-oxidation. Okumoto et al. (2011) reported that siRNA knockdown of LONP2 (referred to as PsLon) in cultured cells caused a measurable decrease in VLCFA β-oxidation flux (pmc.ncbi.nlm.nih.gov). Specifically, the rate of peroxisomal oxidation of a very-long-chain fatty acid substrate was partially reduced when LONP2 was silenced (and significantly reduced when TYSND1 was silenced) (pmc.ncbi.nlm.nih.gov). This partial defect in LONP2 knockdown cells likely results from the accumulation of uncleared TYSND1 fragments and possibly a less efficient processing of matrix enzymes. In the same study, knockdown of TYSND1 caused accumulation of multiple β-oxidation enzymes in their larger, unprocessed (precursor) forms (pmc.ncbi.nlm.nih.gov), which severely curtailed β-oxidation activity. LONP2 knockdown did not cause such precursor accumulation (consistent with LONP2 not directly processing those enzymes), but it did allow buildup of TYSND1 fragments (pmc.ncbi.nlm.nih.gov). The data suggest a model wherein TYSND1 and LONP2 cooperatively regulate the fatty acid β-oxidation pathway: TYSND1 activates enzymes by cleaving them, and LONP2 then degrades TYSND1’s by-products and possibly inactivates TYSND1 itself when appropriate, to fine-tune protease levels (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). In this way, LONP2 indirectly “may regulate peroxisomal fatty acid β-oxidation through degradation of the self-processed forms of TYSND1” (www.genecards.org). Supporting this, an earlier rat study identified Lon protease in liver peroxisomes but noted its substrates “had yet to be defined” (pmc.ncbi.nlm.nih.gov). Okumoto’s work filled that gap by defining TYSND1 (and by extension the enzymes TYSND1 processes, like ACOX1) as part of LONP2’s substrate network.

Beyond fatty acid metabolism, perturbation of LONP2 affects other metabolic and signaling pathways linked to peroxisome function. Peroxisomes are involved in biosynthesis of bile acids, ether phospholipids (plasmalogens), and in reactive oxygen signaling, among other roles (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com). A striking recent finding is that LONP2 depletion can influence cellular lipid trafficking and signaling. In the 2023 study by Bailey et al., LONP2 knockdown in mammalian cells led to cholesterol accumulation in endosomal/lysosomal compartments (biologydirect.biomedcentral.com). This aligns with emerging evidence that peroxisomes facilitate cholesterol efflux from lysosomes (for example, through membrane contacts) (biologydirect.biomedcentral.com). When peroxisomal proteostasis is upset by LONP2 loss, cholesterol appears to get “stuck” in late endosomes/lysosomes, highlighting a previously underappreciated link between peroxisomal health and cholesterol homeostasis (biologydirect.biomedcentral.com). The same study also found that retinoic acid signaling pathways were down-regulated in LONP2-deficient cells, and sphingolipid levels were up-regulated (biologydirect.biomedcentral.com). Retinoic acid (a derivative of vitamin A) is partly metabolized in peroxisomes, so a dysfunction in peroxisomes could blunt RA signaling by altering RA availability or turnover. Increased sphingolipids might reflect a stress response or compensatory change in membrane composition when cholesterol handling is impaired. Together, these data indicate that peroxisomal stress caused by LONP2 loss can ripple out to broader cellular metabolism, affecting lipid distribution and signaling networks (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com).

Another major consequence of LONP2 dysfunction is the activation of cellular stress responses. When misfolded proteins accumulate in an organelle, cells often trigger signaling pathways to restore homeostasis (e.g. the unfolded protein response in ER or mitochondria). A parallel is now observed for peroxisomes: LONP2 silencing elicits an integrated stress response (ISR) in certain contexts. Specifically, in COS-7 cells (monkey kidney cells), loss of LONP2 led to a strong phosphorylation of eIF2α and upregulation of genes involved in stress and ribosome biogenesis, hallmark features of the ISR (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com). This suggests that “peroxisomal proteotoxic stress” (accumulation of unfolded proteins in peroxisomes due to LONP2 impairment) can communicate with the cytoplasm/nucleus to slow down protein synthesis and adjust gene expression. Interestingly, the stress response was somewhat cell-type-specific: COS-7 cells showed a robust ISR, whereas human U2OS cells (an osteosarcoma line) had a more muted ISR, though both cell types shared some responses (like the lipid changes mentioned) (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com). Both cell types, however, engaged transcriptional changes rather than immediately resorting to wholesale peroxisome degradation, indicating the cell attempts to mitigate the protein-folding stress by altering metabolism and gene expression when LONP2 is deficient.

Biological and Clinical Significance

Considering its fundamental role, LONP2 is crucial for the longevity and adaptability of peroxisomes. Some expert reviews have highlighted Lon proteases as critical “aging guardians” of organelle function. The mitochondrial Lon (LonP1) has long been known to decline with age and to be important for handling oxidative stress in aging cells (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). By analogy, peroxisomal LonP2 is thought to protect cells from age-related damage: peroxisomes in older organisms often show functional decline, and accumulation of oxidized peroxisomal proteins could contribute to cellular aging if not counteracted (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Indeed, peroxisomal dysfunction has been associated with age-related diseases (neurodegeneration, metabolic syndrome), and maintaining peroxisomal proteostasis is proposed to be a component of “healthy aging” (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). While direct studies of LonP2 in aging are still emerging, its role in preventing oxidative protein damage places it at the heart of preserving peroxisomal function over time (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). For example, in rodent models of peroxisome stress, young animals show higher LonP2 levels/activity compared to older ones (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov), hinting that LonP2 may diminish with age similarly to LonP1. If so, boosting LonP2 function might be a future avenue to mitigate age-related peroxisomal defects.

From a clinical perspective, genetic disruption of LONP2 in humans is rare but informative. Until recently, no classic peroxisomal biogenesis disorder was linked to LONP2, likely because peroxisomes can form normally and perform many functions even if proteostasis is suboptimal. However, in 2021 a new autosomal dominant neurodevelopmental disorder called Buratti-Harel Syndrome (BURHAS) was attributed to de novo mutations in LONP2 (www.malacards.org) (www.malacards.org). This syndrome is characterized by infantile hypotonia, delayed motor and speech milestones, mild to moderate intellectual disability, and subtle dysmorphic features (www.malacards.org). Notably, it is relatively mild compared to classical peroxisomal disorders (patients survive to childhood and can attend special schooling) (www.malacards.org). The causative LONP2 variants are heterozygous, suggesting a dominant-negative effect or haploinsufficiency. The fact that partial loss of LONP2 leads to neurological development issues underscores the enzyme’s importance in certain tissues (potentially the brain). It implies that peroxisomal protein quality control is especially vital for neuronal cells, which are highly sensitive to metabolic and oxidative imbalances. Aside from this rare syndrome, LONP2 has also been implicated as a gene of interest in cancer genomics (e.g. a correlation with bladder cancer in some datasets) (www.genecards.org), though such associations are still preliminary. In cell models, LONP2 loss did increase oxidative stress in mitochondria (at least in some cell types) (biologydirect.biomedcentral.com) and altered lipid signaling, which could conceivably contribute to pathologies if chronic. Nonetheless, no common diseases have yet been directly tied to LONP2 dysfunction, and Buratti-Harel syndrome remains the clearest example of its impact in humans.

In summary, LONP2 is an essential proteolytic guardian of the peroxisome. It catalyzes the ATP-dependent degradation of aberrant proteins in the peroxisomal matrix, with a substrate preference for oxidized or misfolded polypeptides (www.genecards.org) (pmc.ncbi.nlm.nih.gov). Through this activity (and auxiliary chaperone functions), LONP2 preserves the functional proteome of peroxisomes, enabling these organelles to carry out vital metabolic processes like fatty acid β-oxidation and peroxisomal ROS detoxification (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). It works in concert with the peroxisome-specific protease TYSND1 – together, these two proteases orchestrate the maturation and turnover of key enzymes, thereby regulating metabolic flux through peroxisomal pathways (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). LONP2’s importance is further highlighted by cellular stress responses that emerge when it is absent: peroxisome morphology changes, import mechanisms falter, and stress signals (like the ISR) activate to compensate (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com). By preventing toxic protein aggregation, LONP2 also forestalls the need for wholesale organelle degradation, integrating into the cell’s broader quality control network alongside autophagy (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Given its critical role in maintaining peroxisomal health, LONP2 is increasingly a focus of research not only for understanding peroxisome biology but also for its potential links to aging and disease. As one review succinctly stated, “the peroxisome-specific Lon protease plays a major role in maintaining peroxisomal protein homeostasis” and provides a crucial mechanism to avoid oxidative damage accumulation inside the organelle (pmc.ncbi.nlm.nih.gov). This protective function of LONP2 ultimately supports the versatility and longevity of peroxisomes, ensuring they can meet the cell’s metabolic and signaling needs without succumbing to the very oxidative pressures they generate.

References:

1. Pomatto, L.C.D., et al. (2017). The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1. Biol. Rev. 92(2):739–753 (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

2. Bartoszewska, M., et al. (2012). Peroxisomal proteostasis involves a Lon family protein that functions as protease and chaperone. J. Biol. Chem. 287(33):27380–27395 (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

3. Okumoto, K., et al. (2011). Two proteases, trypsin domain–containing 1 (Tysnd1) and peroxisomal Lon protease (PsLon), cooperatively regulate fatty acid β-oxidation in the peroxisomal matrix. J. Biol. Chem. 286(52):44367–44379 (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

4. Bailey, L.J., et al. (2023). Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism. Biology Direct 18:60 (biologydirect.biomedcentral.com) (biologydirect.biomedcentral.com).

5. NCBI Gene ID: 83752 (LONP2) – Gene Summary (Updated Jan 2017) (www.ncbi.nlm.nih.gov).

6. UniProtKB entry Q86WA8 (LONP2_HUMAN) – Swiss-Prot reviewed protein, Lon protease 2 (www.genecards.org) (www.genecards.org).

7. Aksam, E.B., et al. (2007). A peroxisomal Lon protease and peroxisome degradation by autophagy play key roles in vitality of Hansenula polymorpha. Autophagy 3(2):96–105 (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov).

8. GeneCards entry for LONP2 (Lon Peptidase 2, Peroxisomal) – Summary of function and associated pathways (www.genecards.org) (www.genecards.org).

9. MalaCards: Buratti-Harel Syndrome – OMIM summary of clinical features (Buratti et al., 2021) (www.malacards.org) (www.malacards.org).

Citations

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2. AnnotationURLCitation(end_index=713, start_index=546, title='Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism | Biology Direct | Full Text', type='url_citation', url='https://biologydirect.biomedcentral.com/articles/10.1186/s13062-023-00416-3#:~:text=,an%20ATP%20dependent%20protease%20responsible')
3. AnnotationURLCitation(end_index=1150, start_index=987, title='LONP2 lon peptidase 2, peroxisomal [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene/83752#:~:text=In%20human%2C%20peroxisomes%20function%20primarily,provided%20by%20RefSeq%2C%20Jan%202017')
4. AnnotationURLCitation(end_index=1482, start_index=1319, title='LONP2 lon peptidase 2, peroxisomal [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene/83752#:~:text=In%20human%2C%20peroxisomes%20function%20primarily,provided%20by%20RefSeq%2C%20Jan%202017')
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6. AnnotationURLCitation(end_index=1949, start_index=1794, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=In%20cells%20of%20a%20PLN,Pln%20protease%20and%20chaperone%20activities')
7. AnnotationURLCitation(end_index=2233, start_index=2123, title='LONP2 lon peptidase 2, peroxisomal [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene/83752#:~:text=isoforms.%20,Orthologs%20%2013%20all')
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11. AnnotationURLCitation(end_index=3479, start_index=3302, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=quantitative%20measurement%20of%20the%20proteolytic,LonP1%20utilizes%20ATP%20hydrolysis%20not')
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13. AnnotationURLCitation(end_index=4074, start_index=3903, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=Results%3A%20Pln%20is%20an%20ATP,peroxisomes%20that%20compromise%20organelle%20function')
14. AnnotationURLCitation(end_index=4404, start_index=4233, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=Results%3A%20Pln%20is%20an%20ATP,peroxisomes%20that%20compromise%20organelle%20function')
15. AnnotationURLCitation(end_index=4751, start_index=4600, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=We%20show%20that%20Pln%20is,that%20Pln%20has%20chaperone%20activity')
16. AnnotationURLCitation(end_index=4907, start_index=4752, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=In%20cells%20of%20a%20PLN,Pln%20protease%20and%20chaperone%20activities')
17. AnnotationURLCitation(end_index=5431, start_index=5318, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=various%20species%20%28Pln%29')
18. AnnotationURLCitation(end_index=5812, start_index=5657, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=In%20cells%20of%20a%20PLN,Pln%20protease%20and%20chaperone%20activities')
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83. AnnotationURLCitation(end_index=30123, start_index=29950, title='Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism | Biology Direct | Full Text', type='url_citation', url='https://biologydirect.biomedcentral.com/articles/10.1186/s13062-023-00416-3#:~:text=cell,responses%20seen%20in%20peroxisomal%20disorders')
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85. AnnotationURLCitation(end_index=31089, start_index=30931, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=with%20adaptation%20to%20acute%20oxidative,in%20adaptation%20is%20not%20as')
86. AnnotationURLCitation(end_index=31500, start_index=31341, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=Lon%20protease%20that%20is%20responsible,may%20be%20detrimental%20for%20the')
87. AnnotationURLCitation(end_index=31662, start_index=31501, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=stress%20and%20aging%20has%20been,vital%20mechanism%20to%20maintain%20protein')
88. AnnotationURLCitation(end_index=32034, start_index=31873, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=stress%20and%20aging%20has%20been,vital%20mechanism%20to%20maintain%20protein')
89. AnnotationURLCitation(end_index=32218, start_index=32035, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=mitochondria%20and%20peroxisomes%20are%20both,both%20peroxisome%20and%20mitochondrial%20dysfunction')
90. AnnotationURLCitation(end_index=32565, start_index=32395, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=The%20accumulation%20of%20oxidatively%20damaged,related%20diseases%20indicating%20that')
91. AnnotationURLCitation(end_index=32663, start_index=32566, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=1995%20%29,21')
92. AnnotationURLCitation(end_index=32966, start_index=32788, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=degrades%20proteins%20damaged%20by%20reactive,nucleus%20and%20endoplasmic%20reticulum%2C%20the')
93. AnnotationURLCitation(end_index=33125, start_index=32967, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=with%20adaptation%20to%20acute%20oxidative,in%20adaptation%20is%20not%20as')
94. AnnotationURLCitation(end_index=33831, start_index=33734, title='Buratti-Harel Syndrome - MalaCards', type='url_citation', url='https://www.malacards.org/card/buratti_harel_syndrome#:~:text=Buratti,2021')
95. AnnotationURLCitation(end_index=34028, start_index=33832, title='Buratti-Harel Syndrome - MalaCards', type='url_citation', url='https://www.malacards.org/card/buratti_harel_syndrome#:~:text=An%20autosomal%20dominant%20neurodevelopmental%20disorder,development%2C%20and%20dysmorphic%20facial%20features')
96. AnnotationURLCitation(end_index=34292, start_index=34195, title='Buratti-Harel Syndrome - MalaCards', type='url_citation', url='https://www.malacards.org/card/buratti_harel_syndrome#:~:text=Buratti,2021')
97. AnnotationURLCitation(end_index=34531, start_index=34434, title='Buratti-Harel Syndrome - MalaCards', type='url_citation', url='https://www.malacards.org/card/buratti_harel_syndrome#:~:text=Buratti,2021')
98. AnnotationURLCitation(end_index=35247, start_index=35121, title='LONP2 Gene - GeneCards | LONP2 Protein | LONP2 Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=LONP2#:~:text=LONP2%20,of%20this%20gene%20is%20LONP1')
99. AnnotationURLCitation(end_index=35591, start_index=35400, title='Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism | Biology Direct | Full Text', type='url_citation', url='https://biologydirect.biomedcentral.com/articles/10.1186/s13062-023-00416-3#:~:text=match%20at%20L209%20remained%20unchanged,stained%20superoxide%20within')
100. AnnotationURLCitation(end_index=36192, start_index=36087, title='LONP2 Gene - GeneCards | LONP2 Protein | LONP2 Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=LONP2#:~:text=UniProtKB%2FSwiss')
101. AnnotationURLCitation(end_index=36290, start_index=36193, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=1995%20%29,21')
102. AnnotationURLCitation(end_index=36700, start_index=36535, title='Two Proteases, Trypsin Domain-containing 1 (Tysnd1) and Peroxisomal Lon Protease (PsLon), Cooperatively Regulate Fatty Acid β-Oxidation in Peroxisomal Matrix - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3247999/#:~:text=accumulation%20of%20endogenous%20%CE%B2,Tysnd1%20cleavage%20products%20by%20PsLon')
103. AnnotationURLCitation(end_index=36794, start_index=36701, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=%282H_,21')
104. AnnotationURLCitation(end_index=37170, start_index=37016, title='Two Proteases, Trypsin Domain-containing 1 (Tysnd1) and Peroxisomal Lon Protease (PsLon), Cooperatively Regulate Fatty Acid β-Oxidation in Peroxisomal Matrix - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3247999/#:~:text=Results%3A%20Tysnd1%20inactivates%20its%20protease,oxidation%20enzymes')
105. AnnotationURLCitation(end_index=37336, start_index=37171, title='Two Proteases, Trypsin Domain-containing 1 (Tysnd1) and Peroxisomal Lon Protease (PsLon), Cooperatively Regulate Fatty Acid β-Oxidation in Peroxisomal Matrix - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3247999/#:~:text=accumulation%20of%20endogenous%20%CE%B2,Tysnd1%20cleavage%20products%20by%20PsLon')
106. AnnotationURLCitation(end_index=37750, start_index=37554, title='Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism | Biology Direct | Full Text', type='url_citation', url='https://biologydirect.biomedcentral.com/articles/10.1186/s13062-023-00416-3#:~:text=peroxisomal%20proteotoxic%20stress%20upon%20silencing,7%20and%20U2OS%20cell')
107. AnnotationURLCitation(end_index=37959, start_index=37751, title='Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism | Biology Direct | Full Text', type='url_citation', url='https://biologydirect.biomedcentral.com/articles/10.1186/s13062-023-00416-3#:~:text=biogenesis%20gene%20expression%20levels,responses%20seen%20in%20peroxisomal%20disorders')
108. AnnotationURLCitation(end_index=38317, start_index=38150, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=deleting%20the%20homolog%20for%20peroxisomal,accumulation%20of%20high%20levels%20of')
109. AnnotationURLCitation(end_index=38413, start_index=38318, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=survival,63')
110. AnnotationURLCitation(end_index=38949, start_index=38852, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=1995%20%29,21')
111. AnnotationURLCitation(end_index=39564, start_index=39393, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=Peroxisomes%20are%20ubiquitous%20eukaryotic%20organelles,in%20relation%20to%20oxidative')
112. AnnotationURLCitation(end_index=39662, start_index=39565, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=1995%20%29,21')
113. AnnotationURLCitation(end_index=39952, start_index=39839, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=various%20species%20%28Pln%29')
114. AnnotationURLCitation(end_index=40108, start_index=39953, title='Peroxisomal Proteostasis Involves a Lon Family Protein That Functions as Protease and Chaperone - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3431691/#:~:text=In%20cells%20of%20a%20PLN,Pln%20protease%20and%20chaperone%20activities')
115. AnnotationURLCitation(end_index=40500, start_index=40346, title='Two Proteases, Trypsin Domain-containing 1 (Tysnd1) and Peroxisomal Lon Protease (PsLon), Cooperatively Regulate Fatty Acid β-Oxidation in Peroxisomal Matrix - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3247999/#:~:text=Results%3A%20Tysnd1%20inactivates%20its%20protease,oxidation%20enzymes')
116. AnnotationURLCitation(end_index=40666, start_index=40501, title='Two Proteases, Trypsin Domain-containing 1 (Tysnd1) and Peroxisomal Lon Protease (PsLon), Cooperatively Regulate Fatty Acid β-Oxidation in Peroxisomal Matrix - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC3247999/#:~:text=accumulation%20of%20endogenous%20%CE%B2,Tysnd1%20cleavage%20products%20by%20PsLon')
117. AnnotationURLCitation(end_index=41052, start_index=40856, title='Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism | Biology Direct | Full Text', type='url_citation', url='https://biologydirect.biomedcentral.com/articles/10.1186/s13062-023-00416-3#:~:text=peroxisomal%20proteotoxic%20stress%20upon%20silencing,7%20and%20U2OS%20cell')
118. AnnotationURLCitation(end_index=41261, start_index=41053, title='Depletion of LONP2 unmasks differential requirements for peroxisomal function between cell types and in cholesterol metabolism | Biology Direct | Full Text', type='url_citation', url='https://biologydirect.biomedcentral.com/articles/10.1186/s13062-023-00416-3#:~:text=biogenesis%20gene%20expression%20levels,responses%20seen%20in%20peroxisomal%20disorders')
119. AnnotationURLCitation(end_index=41492, start_index=41329, title='LONP2 lon peptidase 2, peroxisomal [Homo sapiens (human)] - Gene - NCBI', type='url_citation', url='https://www.ncbi.nlm.nih.gov/gene/83752#:~:text=In%20human%2C%20peroxisomes%20function%20primarily,provided%20by%20RefSeq%2C%20Jan%202017')
120. AnnotationURLCitation(end_index=41686, start_index=41581, title='LONP2 Gene - GeneCards | LONP2 Protein | LONP2 Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=LONP2#:~:text=UniProtKB%2FSwiss')
121. AnnotationURLCitation(end_index=41805, start_index=41687, title='LONP2 Gene - GeneCards | LONP2 Protein | LONP2 Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=LONP2#:~:text=ATP,%28%20LONP2_HUMAN%2CQ86WA8')
122. AnnotationURLCitation(end_index=42153, start_index=41986, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=deleting%20the%20homolog%20for%20peroxisomal,accumulation%20of%20high%20levels%20of')
123. AnnotationURLCitation(end_index=42311, start_index=42154, title='The peroxisomal Lon protease LonP2 in aging and disease: functions and comparisons with mitochondrial Lon protease LonP1 - PMC', type='url_citation', url='https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/#:~:text=In%20addition%2C%20pln%20and%20pln,This%20downstream%20effect%20resulting')
124. AnnotationURLCitation(end_index=42546, start_index=42420, title='LONP2 Gene - GeneCards | LONP2 Protein | LONP2 Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=LONP2#:~:text=LONP2%20,of%20this%20gene%20is%20LONP1')
125. AnnotationURLCitation(end_index=42652, start_index=42547, title='LONP2 Gene - GeneCards | LONP2 Protein | LONP2 Antibody', type='url_citation', url='https://www.genecards.org/cgi-bin/carddisp.pl?gene=LONP2#:~:text=UniProtKB%2FSwiss')
126. AnnotationURLCitation(end_index=42848, start_index=42751, title='Buratti-Harel Syndrome - MalaCards', type='url_citation', url='https://www.malacards.org/card/buratti_harel_syndrome#:~:text=Buratti,2021')
127. AnnotationURLCitation(end_index=43045, start_index=42849, title='Buratti-Harel Syndrome - MalaCards', type='url_citation', url='https://www.malacards.org/card/buratti_harel_syndrome#:~:text=An%20autosomal%20dominant%20neurodevelopmental%20disorder,development%2C%20and%20dysmorphic%20facial%20features')

The LONP2 (Q86WA8) gene encodes a peroxisomal ATP-dependent serine protease involved in the selective degradation of misfolded and oxidized proteins within the peroxisomal matrix, contributing to peroxisome homeostasis and protein quality control[1][2][9].

Key Concepts and Definitions

• Molecular Function:
• ATP-dependent serine protease: LONP2 hydrolyzes ATP to drive the degradation of misfolded, unassembled, or oxidatively damaged polypeptides in the peroxisomal matrix[1][2][9].
• Chaperone activity: It may also function as a peroxisomal chaperone, assisting in protein folding and import[5].

• GO Annotations: Includes ATP hydrolysis activity and signaling receptor binding[1][10].

• Biological Processes:

• Protein quality control: Degrades damaged peroxisomal proteins, especially those affected by oxidative stress, maintaining peroxisome function[1][2][8].
• Peroxisomal protein import: Facilitates processing and import of proteins with type 2 peroxisome targeting signals (PTS2)[1][9].
• Fatty acid beta-oxidation regulation: Indirectly regulates peroxisomal fatty acid metabolism by degrading processed forms of TYSND1, a peroxisomal protease[1][9].

• Oxidative stress response: Highly expressed in tissues with high oxidative metabolism (pancreas, kidney, liver), where it helps prevent protein aggregation due to oxidative damage[2].

• Cellular Localization:

• Peroxisomal matrix: LONP2 is targeted to the peroxisome via a C-terminal peroxisome targeting signal (PTS1), and concentrates within the dense crystalline core of the peroxisome[2][4][9].
• Ubiquitous expression: Found throughout the body, with highest levels in pancreas, kidney, and liver[2].

Protein Domains

• N-terminal Lon N domain: Substrate recognition, binds oxidized proteins[1][2][12].
• ATPase domain (AAA+): Contains Walker A and B motifs, responsible for ATP hydrolysis[2][12].
• Proteolytic domain: Contains a serine–lysine dyad for enzymatic degradation of substrates[2][12].
• C-terminal peroxisome targeting sequence (PTS1): Directs the protein to the peroxisome[1][2].

Known Interactions

• TYSND1: LONP2 degrades self-processed forms of TYSND1, a peroxisomal protease involved in protein import and processing[1][9].
• PEX5 (PTS1 receptor): Works in concert with peroxisomal import machinery for processing PTS2-containing proteins[13].
• Other peroxisomal proteins: Likely interacts with various oxidized or misfolded peroxisomal matrix proteins as substrates[2][5].

Disease Associations

• Buratti-Harel Syndrome: Mutations in LONP2 are associated with this rare genetic disorder[1].
• Bladder Cancer: LONP2 has been implicated in the pathogenesis of bladder cancer[1].
• Cervical Tumorigenesis: Recent studies suggest LONP2 promotes cervical cancer development via modulation of oxidative stress[14].
• General cancer biology: Dysregulation of LONP2 may contribute to tumorigenesis by affecting cellular oxidative stress and protein homeostasis[14].

Recent Developments and Latest Research (2023–2024)

• Cancer research: LONP2 is being investigated as a potential biomarker and therapeutic target in cancers, particularly those with high oxidative stress environments[14].
• Functional studies: Ongoing research is characterizing the specific substrates and regulatory mechanisms of LONP2 in peroxisomal protein quality control[12].
• Variant analysis: AI-powered platforms are being used to analyze LONP2 variants for disease association and functional impact[8].

Real-World Applications

• Disease diagnostics: LONP2 expression and mutation status may be used in diagnostic panels for certain cancers and genetic syndromes[1][14].
• Therapeutic targeting: Modulation of LONP2 activity is being explored for diseases involving peroxisomal dysfunction or oxidative stress[14].

Expert Opinions and Authoritative Analysis

• GeneCards, UniProt, and NCBI consistently describe LONP2 as essential for peroxisomal protein quality control and homeostasis[1][9][14].
• Recent reviews highlight its role in aging, oxidative stress response, and disease, especially in tissues with high metabolic activity[2].

Relevant Statistics and Data

• Protein size: 852 amino acids, ~95 kDa[2].
• Expression: Highest in pancreas, kidney, and liver[2].
• Genomic location: Chromosome 16[2][14].

URLs and Publication Dates

• GeneCards LONP2 (2024)
• PMC: The peroxisomal Lon protease LonP2 in aging and disease (2016, cited in recent reviews)
• UniProt Q86WA8 (2024)
• NCBI Gene 83752 (2024)
• AI-Powered Variant Analysis Platform (2024)
• Human Protein Atlas (2024)

If you require more detailed information on specific variants, experimental data, or clinical studies, these resources provide up-to-date datasets and publications.

Citations

1. https://www.genecards.org/cgi-bin/carddisp.pl?gene=LONP2
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC5159316/
3. https://en.wikipedia.org/wiki/Lon_peptidase_2,_peroxisomal
4. https://www.proteinatlas.org/ENSG00000102910-LONP2
5. https://marrvel.org/human/gene/83752
6. http://flybase.org/reports/FBGN0036892
7. https://portal.gdc.cancer.gov/genes/ENSG00000102910
8. https://rddc.tsinghua-gd.org/gene/83752
9. https://www.uniprot.org/uniprotkb/Q86WA8/entry
10. https://www.ebi.ac.uk/QuickGO/GProtein?ac=Q86WA8
11. https://functionome.geneontology.org/gene/UniProtKB:Q86WA8
12. https://research.kuleuven.be/portal/en/project/3M240063
13. https://www.uniprot.org/uniprotkb/Q86WA8/publications
14. https://www.ncbi.nlm.nih.gov/gene/83752
15. https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000102910

Comprehensive Functional Annotation of LONP2: The Peroxisomal Lon Peptidase 2 in Human Biology

This report presents a detailed analysis of LONP2 (Lon peptidase 2, peroxisomal), encoded by the human LONP2 gene located on chromosome 16, with comprehensive coverage of its enzymatic function, structural organization, subcellular localization, metabolic roles, and involvement in both physiological and pathological processes. LONP2 is an ATP-dependent serine protease that serves as a critical regulator of peroxisomal protein quality control through selective degradation of misfolded and oxidatively damaged proteins. Operating within the peroxisomal matrix, particularly concentrated in the crystalline core where oxidative stress is most pronounced, LONP2 functions as both a protease and molecular chaperone to maintain protein homeostasis in this essential metabolic organelle. Beyond its canonical proteolytic role, emerging evidence demonstrates that LONP2 regulates peroxisomal fatty acid beta-oxidation, participates in lipid metabolism pathways, and influences cellular responses to oxidative stress. Furthermore, dysregulation of LONP2 expression and activity has been associated with multiple disease states including cervical carcinogenesis, endothelial dysfunction, and the neurodevelopmental disorder Buratti-Harel Syndrome. This comprehensive review synthesizes current understanding of LONP2 structure, function, regulation, and disease relevance based on experimental evidence, structural analysis, and evolutionary considerations.

Structural Organization and Molecular Characterization of LONP2

Primary Structure and Evolutionary Conservation

The human LONP2 protein is composed of 852 amino acids with a calculated molecular weight of approximately 95 kilodaltons in its mature form[12]. LONP2 belongs to the Lon A family of proteases, representing the primary form of Lon protease found across prokaryotes and eukaryotes[12]. The protein is encoded by the LONP2 gene from the nuclear genome on chromosome 16 and is synthesized on free ribosomes in the cytoplasm before being targeted to the peroxisomal compartment[12]. The evolutionary origin of LONP2 is particularly notable, as it represents an early gene duplication product of the mitochondrial LONP1 protease that was retained and specialized for peroxisomal function[53]. While LONP2 has been identified in diverse organisms including mammals, yeast, nematodes, and fungi such as Phaffia chrysogenum and Hansenula polymorpha, suggesting conservation across eukaryotic life, the peroxisomal Lon isoform appears less universally conserved than its mitochondrial counterpart, having not been physically detected in Drosophila melanogaster despite extensive characterization in most other model organisms[30].

Functional Domains and Catalytic Architecture

The LONP2 protein exhibits a highly organized multi-domain architecture that orchestrates its diverse enzymatic and chaperone functions[12]. The N-terminal region contains the Lon N substrate recognition domain, which operates through a non-catalytically active serine residue that facilitates substrate binding rather than catalysis[12]. This substrate recognition domain plays a critical role in identifying target proteins for degradation and has been shown to be important for dodecamer assembly in related Lon proteases, suggesting that it may modulate substrate specificity through conformational changes[31]. The central ATPase domain contains the canonical Walker A and B motifs characteristic of AAA+ (ATPases Associated with diverse cellular Activities) proteases[12]. These Walker motifs are conserved three-dimensional protein structures that mediate ATP binding and hydrolysis, allowing LONP2 to harness the energy of ATP to power substrate unfolding and translocation[12]. The carboxyl-terminal proteolytic domain contains the catalytically active serine-lysine dyad responsible for peptide bond cleavage[12]. This serine-lysine catalytic pair represents a unique mechanistic approach among serine proteases, where the lysine acts as a general base to activate the serine nucleophile for attack on the carbonyl carbon of the scissile peptide bond[45].

Peroxisomal Targeting and Subcellular Localization

LONP2 contains a C-terminal peroxisomal targeting signal (PTS1) consisting of the characteristic SKL (serine-lysine-leucine) or variant motif that directs the protein to peroxisomes[12]. The PTS1 sequence is recognized by the peroxisomal import receptor Pex5, which shuttles LONP2 across the peroxisomal membrane into the matrix[18]. Critically, unlike most organellar import signals that are removed during or immediately after translocation, the PTS1 sequence of LONP2 is preserved upon import into the peroxisome, suggesting that this targeting information may serve additional regulatory functions beyond initial targeting[18]. Ultracentrifugation studies using antibodies raised against the C-terminal region of LONP2 have demonstrated that this protease not only localizes to the peroxisomal matrix but specifically concentrates within the dense crystalline core of the organelle[30]. This concentration pattern is particularly instructive regarding LONP2's functional role. The crystalline core of mammalian liver peroxisomes is primarily composed of urate oxidase and is notably devoid of catalase and other oxidases[30]. Consequently, hydrogen peroxide accumulates in this sub-compartment and cannot be effectively degraded, leading to rapid oxidative damage of proteins in close proximity. The strategic positioning of LONP2 in this highly oxidizing microenvironment parallels the localization of mitochondrial Lon protease (LonP1) near the inner mitochondrial membrane, where both enzymes maintain high concentration and close proximity to proteins at risk of oxidative damage requiring rapid degradation[30].

In mammalian tissues, LONP2 is ubiquitously distributed throughout the body, with particularly elevated expression patterns in organs with high metabolic activity and oxidative burden[30]. Specifically, the pancreas, kidney, and liver show the highest levels of LONP2 expression[30], consistent with the lipid-metabolizing and energy-producing functions of these tissues. Additional analysis of tissue-specific expression patterns indicates substantial representation in tissues with specialized lipid metabolism requirements, including multiple brain regions, adipose tissue, and reproductive organs where ether lipid biosynthesis and fatty acid oxidation are particularly important[6].

Enzymatic Function and Substrate Specificity of LONP2

ATP-Dependent Proteolytic Mechanism

LONP2 functions as an ATP-dependent protease that mediates the selective degradation of misfolded and unassembled polypeptides within the peroxisomal matrix[4][10]. A fundamental characteristic of LONP2 as an ATP-dependent enzyme is that ATP hydrolysis is absolutely essential for proteolytic activity; in the absence of ATP, LONP2 exhibits less than 3% of its normal enzymatic activity[55]. The ATP-stimulated activity of LONP2 was originally discovered through in vitro studies employing the fungus Phaffia chrysogenum, where purified LONP2 rapidly degraded misfolded model substrates such as α-casein and β-casein specifically in the presence of ATP[7]. Quantitative measurements using resorufin-labeled β-casein as a fluorescent substrate demonstrated that LONP2 exhibited high proteolytic activity only upon ATP addition, establishing the strict requirement for ATP in the catalytic cycle[7]. As definitive proof of principle, mutagenesis of the catalytically active serine residue in the proteolytic domain rendered the enzyme completely non-functional, preventing substrate degradation even in the presence of both misfolded casein and ATP[7]. This catalytic mechanism whereby LONP2 utilizes ATP hydrolysis for substrate degradation appears to differ functionally from mitochondrial LonP1, which uses ATP hydrolysis to induce conformational changes in the proteolytic site rather than for direct substrate degradation[7]. Future studies employing non-hydrolysable ATP analogs are anticipated to clarify whether LONP2 uses ATP as a true substrate cofactor for degradation reactions or in a role more similar to LonP1's conformational activation mechanism.

Substrate Recognition and Protein Specificity

The primary substrates targeted for degradation by LONP2 are proteins bearing oxidative damage or those misfolded due to post-translational processing defects. The recognition mechanism employed by LONP2 relies on the Lon N substrate recognition domain binding to oxidized proteins in which hydrophobic residues normally buried in the native protein core become exposed through protein unfolding[7]. This recognition pattern indicates that LONP2 functions as a general oxidative damage sensor rather than recognizing specific sequence motifs or structured domains. The binding of oxidized substrates to the non-catalytic serine residue in the Lon N domain facilitates productive enzyme-substrate complex formation that positions the substrate for translocation through the central pore of the LONP2 oligomer and into the catalytic chamber where proteolysis occurs[7].

Experimentally identified substrates of LONP2 in mammalian cells include the serine protease trypsin domain-containing 1 (Tysnd1), which itself is responsible for processing peroxisomal enzymes including acyl-coenzyme A oxidase 1 (ACOX1)[50][53]. The relationship between LONP2 and Tysnd1 is particularly notable; Tysnd1 undergoes self-cleavage to generate inactive fragments, which are subsequently degraded by LONP2[18]. This degradation may not reflect a specific substrate-enzyme pairing but rather LONP2's general affinity for proteins displaying exposed hydrophobic residues characteristic of proteolytic cleavage products and damaged proteins[18]. Additional characterized LONP2 substrates identified in fungal systems include catalase, the most abundant peroxisomal antioxidant, which undergoes oxidative damage and functional loss even at relatively low hydrogen peroxide concentrations[7]. Even at concentrations as low as 100 micromolar H₂O₂, catalase can experience approximately 40% loss of enzymatic function, and higher H₂O₂ levels exacerbate both catalase dysfunction and accumulation of non-functional proteins[7]. The peroxisome maintains high catalase concentrations and relies substantially on LONP2-mediated degradation of dysfunctional catalase to mitigate this progressive loss of catalytic capacity[7].

The substrate specificity of LONP2 appears to be primarily determined by exposure of hydrophobic amino acid residues rather than recognition of structured degron sequences, suggesting broad substrate range encompassing all oxidatively damaged peroxisomal proteins. This mechanism provides the peroxisomal matrix with a flexible quality control system capable of responding to diverse types of oxidative damage rather than requiring pre-specified targeting sequences for each substrate.

Chaperone Functions and Protein Homeostasis Maintenance

ATP-Independent Chaperone Activity

Beyond its primary role as a protease, LONP2 possesses distinct chaperone-like activity that operates independently of ATP hydrolysis and contributes to overall peroxisomal protein quality control[28]. When purified LONP2 was incubated with denatured citrate synthase under experimental conditions, the presence of Lon, independent of ATP, decreased protein aggregation by approximately 40% compared to control samples lacking the protease[28]. Complete inhibition of protein aggregation was achieved through increasing LONP2 concentrations, and enzymatic activity of the denatured substrate protein was successfully re-established following ATP addition, demonstrating that aggregation prevention occurred through a chaperone mechanism rather than through proteolytic degradation[28]. These findings establish that LONP2 possesses multifunctional characteristics, combining both ATP-dependent proteolytic and ATP-independent chaperone activities in a single polypeptide[28]. Unlike mitochondria, which contain comprehensive protein folding machinery including heat shock response proteins such as Hsp60 and mtHsp70, peroxisomes appear to lack dedicated chaperone systems, potentially because proteins are typically imported as fully folded entities[28]. The evolution of LONP2 as a bifunctional protein capable of acting as both an ATP-dependent protease and an ATP-independent chaperone may therefore represent an adaptation to the unique protein homeostasis requirements of the peroxisomal compartment[28].

The relationship between these two activities appears to be dynamically regulated according to cellular requirements[28]. During peroxisome biogenesis and normal metabolic states, the ATP-independent chaperone activity of LONP2 may assist in the correct folding and assembly of newly imported proteins. During periods of decreased metabolic need or in response to oxidative stress, the proteolytic activity of LONP2 becomes dominant, facilitating removal of unnecessary peroxisomal proteins through a combination of direct proteolysis and activation of autophagy-based degradation pathways including pexophagy[28]. This dynamic modulation of protease versus chaperone activity in response to metabolic state represents a sophisticated regulatory mechanism for peroxisomal homeostasis.

Prevention of Protein Aggregation and Inclusion Body Formation

The pathological consequences of LONP2 loss extend to accumulation of insoluble protein aggregates and inclusion bodies within the peroxisomal matrix. Studies in the fungus Phaffia chrysogenum harboring deletion mutations of the peroxisomal Lon gene (pln) demonstrated marked increases in the accumulation of electron-dense protein aggregates, accompanied by increased peroxisome number and enlargement[30]. These protein aggregates were characterized as likely substrates for normal LONP2 degradation, indicating that loss of LONP2 directly results in accumulation of misfolded protein polymers[30]. This phenotype parallels the protein aggregates that arise in Caenorhabditis elegans mutants lacking the mitochondrial Lon homologue (PIM1), as well as in senescent cells lacking mitochondrial Lon activity, suggesting conservation of this quality control function across both organellar compartments and evolutionary distance[30]. The significance of preventing aggregate formation is underscored by the observation that protein aggregates are prevalent markers in senescent cells and are associated with cellular dysfunction, suggesting that LONP2-mediated prevention of aggregation is critical for maintaining peroxisomal and cellular health throughout the lifespan[30].

Biological Roles in Peroxisomal Fatty Acid Metabolism

Integration with Beta-Oxidation Pathways

Peroxisomes function as essential sites for the initial oxidation of very-long-chain fatty acids (VLCFAs) containing 20 or more carbons, as well as branched-chain and di- or tri-hydroxylated fatty acids that cannot be processed by mitochondrial beta-oxidation machinery[11][39]. The primary peroxisomal role in human physiology is catalyzing fatty acid beta-oxidation and, as a necessary byproduct of this oxidative process, generating both hydrogen peroxide and superoxide[2][5]. LONP2 maintains the functionality of this critical metabolic pathway by proteolytically degrading peroxisomal proteins damaged by the oxidative stress inherent to beta-oxidation. Through studies employing gene knockout approaches, LONP2 depletion has been shown to impair peroxisomal fatty acid metabolism through both direct proteolytic effects and indirect metabolic disruption[20]. The degradation of TYSND1 by LONP2 is particularly relevant to fatty acid metabolism maintenance; TYSND1 itself is responsible for the specific processing and post-translational modification of peroxisomal beta-oxidation enzymes, particularly ACOX1[18]. Loss of TYSND1 processing by LONP2 results in accumulation of immature beta-oxidation enzymes and diminished processing capacity for long-chain fatty acids[18][20].

Recent lipidomic analysis of cells with LONP2 silencing revealed dramatic alterations in lipid composition, including accumulation of very-long-chain fatty acid-containing lipids, altered phosphatidylcholine composition reflecting substantial fatty acyl side-chain remodeling, and increased sphingomyelins and cholesterol esters[20][36]. These lipidomic changes were notable for being partially cell-type specific, with COS-7 cells and U2OS cells showing different magnitudes and patterns of lipid disruption despite similar peroxisomal morphological changes[20][36]. This differential response suggests that peroxisomes exhibit substantial functional plasticity depending on tissue context and that the specific consequences of peroxisomal LONP2 loss may vary based on the particular lipid metabolic demands of different cell types and tissues[36].

PTS2 Protein Processing and Import Regulation

LONP2 plays a direct role in peroxisomal protein import regulation through its involvement in processing peroxisomal targeting signal 2 (PTS2) containing proteins[15]. PTS2 represents the less common peroxisomal targeting sequence, comprising nine amino acids located on the N-terminus of target proteins and recognized by the PTS2 receptor Pex7[18]. Following translocation across the peroxisomal membrane, PTS2 sequences are often removed through proteolytic cleavage of the N-terminal targeting propeptide, and LONP2 may participate in this maturation process[27]. The functional significance of this PTS2-associated proteolysis appears to facilitate accumulation of processed proteins within the peroxisomal matrix by removing targeting sequences that otherwise might recycle these proteins back to the cytosol in complex with their import receptors[27]. For PTS1 proteins, the functional significance of peroxisomal processing remains less completely understood, as many PTS1 signal sequences are preserved following translocation and numerous PTS1-containing proteins remain catalytically active without proteolytic maturation, suggesting that processing may serve regulatory rather than activation functions[27].

Regulation of Cellular Redox Homeostasis and Oxidative Stress Response

Peroxisomal Contribution to Cellular ROS Generation and Management

Peroxisomes constitute a major but often underappreciated source of cellular oxidative stress, accounting for approximately 20% of total cellular oxygen consumption and contributing 35% of total hydrogen peroxide generation in mammalian tissues[11][23]. This substantial ROS production results from both the inevitable byproducts of fatty acid beta-oxidation (hydrogen peroxide) and from multiple peroxisomal oxidases including acyl-CoA oxidases and other oxidative enzymes that generate reactive oxygen species including superoxide and hydroxyl radicals as functional byproducts[11][23]. To maintain cellular homeostasis in the face of this oxidative burden, peroxisomes contain a sophisticated antioxidant defense system comprising catalase (the most abundant peroxisomal antioxidant and sole enzyme capable of catalyzing H₂O₂ dismutation), superoxide dismutase 1 (SOD1), peroxiredoxin 5 (Prx5), S-transferase kappa, epoxide hydrolase, and glutathione peroxidase (GPx)[11][23]. Notably, LonP2 has recently been identified alongside insulin-degrading enzyme and PEX11β as a peroxisomal protein that contributes to maintenance of peroxisomal redox homeostasis through mechanisms that extend beyond the canonical antioxidant enzymatic systems[11][23].

The accumulation of oxidatively damaged proteins within peroxisomes represents a critical threat to organellar and cellular function. Deficiencies in peroxisomal antioxidant proteins such as catalase can perturb the mitochondrial redox potential, indicating that peroxisomal dysfunction triggers effects that propagate to the mitochondrial compartment[11][23]. Furthermore, local oxidative damage to peroxisomes eventually results in mitochondrial dysfunction and cellular apoptosis, implicating peroxisomes as upstream initiators of mitochondrial ROS signaling and suggesting that peroxisomal quality control is paramount to cellular survival[11][23]. LONP2's role in preventing oxidative protein damage accumulation within peroxisomes is therefore critical to maintaining not only peroxisomal integrity but also broader cellular redox balance and mitochondrial function.

Evidence for Proteotoxic Stress in LONP2-Deficient Cells

Recent mammalian cell studies employing acute LONP2 silencing via siRNA approaches have revealed that loss of LONP2 triggers cell-type-specific stress responses distinct from total loss of peroxisomal protein import[20][25]. In monkey kidney COS-7 cells with LONP2 knockdown, significant accumulation of mitochondrial reactive oxygen species was detected, measured by MitoSOX staining[25]. Additionally, LONP2-depleted COS-7 cells activated the integrated stress response (ISR), an evolutionary conserved eukaryotic signaling pathway that attenuates cap-dependent translation through phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α)[25]. This ISR activation was accompanied by induction of multiple ISR effector transcription factors (ATF3, ATF4, ATF5, and CHOP encoded by DDIT3) and their downstream targets[25]. Consistent with ISR activation, dramatic reduction of protein synthesis was detected in LONP2-depleted COS-7 cells through puromycin pulse-labeling, a key consequence of eIF2α phosphorylation[25]. Global cellular stress in LONP2-depleted COS-7 cells was further evidenced by activation of apoptosis-associated cleaved caspases 3 and 7, increased DNA damage as monitored by γ2HAX phosphorylation, and induction of NF-κB, a regulator of innate immunity[25]. Remarkably, identical LONP2 depletion in human U2OS osteosarcoma cells did not induce these stress responses, demonstrating that the proteotoxic peroxisomal stress response activates the ISR in a cell-type-specific manner[25]. This differential response likely reflects distinct peroxisomal metabolic demands in different cell types, with certain tissues exhibiting greater dependence on LONP2-mediated proteostasis.

The differential transcriptomic responses observed between COS-7 and U2OS cells upon LONP2 silencing were striking, with over 7,000 differentially expressed genes identified in COS-7 cells compared to fewer than 300 genes in U2OS cells[25]. COS-7 cells specifically upregulated multiple genes involved in ribosome biogenesis, an unexpected finding given that ribosome biogenesis is generally suppressed under cellular stress conditions[25]. Expression of RRS1, a core mediator of ribosomal assembly, was increased at both the mRNA and protein levels in LONP2-depleted COS-7 cells[25]. This paradoxical upregulation of ribosomal biogenesis genes in the context of overall protein synthesis reduction suggests a complex cellular attempt to restore homeostasis through increased ribosomal capacity. The lipidomic changes described above further highlight that LONP2 loss disrupts multiple interconnected metabolic and signaling pathways depending on cell type and tissue context.

Association with Disease States and Clinical Implications

Buratti-Harel Syndrome and Neurodevelopmental Pathology

LONP2 mutations have been identified as causative genetic variants in Buratti-Harel Syndrome (BURHAS), an autosomal dominant neurodevelopmental disorder characterized by infantile hypotonia, global developmental delay, and impaired intellectual development[26][29]. Affected individuals present with infantile hypotonia apparent from early infancy, generalized developmental delay, and delays in motor, language, and speech development with mildly to moderately impaired intellectual function[26]. Many patients exhibit learning difficulties and attend special education programs, while more severely affected individuals show greater functional impairment[26]. Characteristic dysmorphic facial features include hypertelorism (widely spaced eyes), downslanting palpebral fissures, strabismus, and small low-set ears[26]. Additional clinical features frequently present include laryngomalacia with associated feeding difficulties and distal skeletal anomalies[26]. The association between LONP2 mutations and this neurodevelopmental phenotype implicates peroxisomal quality control specifically in proper brain development and function, suggesting that peroxisomal protein homeostasis is critical during neurodevelopmental processes.

The pathogenic mechanisms by which LONP2 mutations cause neurodevelopmental disease likely involve accumulation of misfolded proteins and oxidatively damaged peroxisomal proteins in neural tissues, particularly given the high metabolic demands and oxidative stress burden of the developing and mature nervous system. However, the precise molecular mechanisms by which LONP2 loss leads to the specific clinical features of BURHAS remain to be fully elucidated, representing an important area for further research.

LONP2 Upregulation and Cervical Carcinogenesis

Multiple lines of evidence demonstrate that LONP2 is significantly upregulated in cervical cancer tissue and contributes to cervical tumorigenesis through mechanisms involving oxidative stress modulation[1][38]. Oncomine database analysis and immunohistochemical examination of tissue microarrays demonstrated that LONP2 expression is significantly upregulated in cervical cancer compared to normal cervical tissue, with expression levels approximately twofold higher in cancerous samples[38]. This upregulation showed significant associations with pathological type, pathological grade, and clinical stage of cervical cancer, though no association was detected with patient age or lymph node metastasis status[38]. Experimental knockdown of LONP2 using RNA interference in cervical cancer cell lines HeLa and SiHa reduced cell proliferation, impaired cell cycle progression, induced apoptosis, and decreased both migration and invasion capacity[38]. Notably, LONP2 knockdown reduced oxidative stress levels within cervical cancer cells as measured by ROS production through immunofluorescence and flow cytometry analysis[38]. These findings suggest that LONP2 promotes cervical tumorigenesis through modulation of intracellular oxidative stress levels, potentially enabling cancer cells to maintain metabolic flexibility and adaptive redox states that support tumor growth and metastatic progression[38].

The mechanism by which increased LONP2 activity supports tumorigenesis appears to involve enhanced degradation of oxidatively damaged proteins that would otherwise accumulate and trigger stress responses limiting cancer cell growth. By maintaining peroxisomal proteostasis despite the elevated metabolic activity and ROS production of cancer cells, LONP2 may enable cancer cells to tolerate the oxidative stress that would otherwise activate growth-limiting stress response pathways. This makes LONP2 a potential biomarker and therapeutic target for cervical cancer treatment[38].

CircRNA-LONP2 and Endothelial Dysfunction in Atherosclerosis

Recent evidence reveals a novel functional role for circular RNA derived from the LONP2 locus (circRNA-LONP2) in modulating endothelial dysfunction and atherosclerosis progression, distinct from the role of linear LONP2 mRNA and protein[8]. Importantly, circRNA-LONP2, but not its linear transcript counterpart, emerged as the major cause of inflammation and oxidative stress in endothelial cells through its modulation of specific signaling pathways[8]. Oscillatory (disturbed) shear stress (OSS), the abnormal blood flow pattern that develops in regions of arterial branching and curvature and drives atherosclerosis development, upregulated circRNA-LONP2 expression in endothelial cells[8]. In contrast, laminar shear stress (LSS), the physiological blood flow pattern that protects arteries from atherosclerosis, downregulated circRNA-LONP2 expression[8]. This regulation of circRNA-LONP2 by hemodynamic shear stress represents a novel molecular mechanism linking blood flow patterns to atherosclerotic disease progression.

The molecular mechanism by which circRNA-LONP2 promotes endothelial inflammation involves suppression of microRNA-200a-3p (miR-200a-3p), which normally targets and degrades messenger RNAs for KEAP1, YAP1, and EZH2[8]. By sequestering miR-200a-3p, circRNA-LONP2 allows accumulation of KEAP1, which maintains the transcription factor NRF2 in an inactivated cytoplasmic state through ubiquitin-mediated degradation[8]. Under normal LSS conditions that reduce circRNA-LONP2, miR-200a-3p is liberated and degrades KEAP1 mRNA, allowing NRF2 to accumulate, translocate to the nucleus, and activate transcription of antioxidant response element-containing genes including HO-1 (heme oxygenase-1)[8]. This NRF2/HO-1 activation pathway suppresses oxidative stress and endothelial inflammation[8]. Conversely, under OSS conditions that upregulate circRNA-LONP2, this protective miR-200a-3p-mediated NRF2 activation is suppressed, leading to increased ROS production and endothelial cell inflammation, processes that accelerate atherosclerosis[8]. The identification of circRNA-LONP2 as a therapeutic target provides potential strategies for atherosclerosis prevention and treatment through endothelial-specific knockdown of circRNA-LONP2 or its downstream targets KEAP1, YAP1, or EZH2[8].

Relationship to Mitochondrial Lon (LonP1) and Functional Divergence

Comparative Structure and Functional Specialization

While LONP2 and mitochondrial Lon protease (LonP1) share substantial structural similarity and evolutionary origin, they exhibit important functional differences that reflect specialization to their respective organellar environments[3][12]. Both LonP1 and LonP2 contain conserved N-domains for substrate recognition, classical ATPase domains containing Walker A and B motifs, and C-terminal proteolytic domains with serine-lysine catalytic dyads[12]. However, a critical functional distinction concerns the role of ATP hydrolysis in catalysis. While both are ATP-stimulated enzymes, LonP1 appears to utilize ATP hydrolysis primarily to induce conformational changes in the proteolytic site to allow for substrate degradation, whereas LONP2 may employ ATP hydrolysis more directly in substrate degradation itself[7]. The exact mechanistic differences remain to be fully clarified through studies employing non-hydrolysable ATP analogs and biochemical analysis of the kinetic pathways.

LonP1 dysfunction has been extensively characterized in aging and disease, with studies establishing the importance of mitochondrial Lon in relation to oxidative stress, aging-related diseases, and cancer[32]. In contrast, little was historically known regarding the specific role of LonP2 in aging and age-related pathological changes in the peroxisome[3]. However, the recent recognition that peroxisome dysfunction is associated with multiple aging-related diseases indicates that peroxisomal protein quality control mechanisms including LONP2-mediated proteolysis represent a critical component of healthy aging[3].

Cross-Compartment Communication and Metabolic Coordination

Although mitochondria and peroxisomes are both essential for fatty acid metabolism, particularly through their coordinated handling of different classes of fatty acids, relatively little work has focused on understanding the relationship between these two organelles or how age-dependent changes in one may detrimentally affect the other[3]. LONP2 and LonP1 may function as communication nodes between these metabolically interdependent organelles. Given the metabolic coordination between peroxisomes and mitochondria in fatty acid oxidation and the shared reliance on ATP-dependent quality control mechanisms, understanding the role of LONP2 in the aging peroxisome may help elucidate cellular causes for both peroxisomal and mitochondrial dysfunction[3]. This represents a promising area for future research into the origins of age-related metabolic decline and associated disease susceptibility.

Emerging Concepts: Peroxisomal Proteostasis as a Systems-Level Regulatory Mechanism

Integration of Multiple Cellular Pathways

Recent findings from transcriptomic and lipidomic studies of LONP2-depleted cells reveal that peroxisomal quality control through LONP2-mediated proteolysis functions not merely as a local compartmental homeostasis mechanism but as an integrator of multiple cellular processes[20][25]. The specific coupling of peroxisomal LONP2 activity to cholesterol trafficking, retinoic acid signaling, and ribosome biogenesis identified in mammalian cells suggests that peroxisomal proteostasis serves as a sensor of organellar metabolic state with outputs affecting multiple signaling and biosynthetic pathways[20][25]. The cell-type-specific nature of responses to LONP2 loss further indicates that the functional consequences of peroxisomal proteostasis are highly context-dependent, potentially explaining why peroxisomal disorders present with tissue-specific pathology.

Evolutionary and Biophysical Insights

The hexameric ring architecture of Lon proteases, shared with other AAA+ proteases, enables formation of higher-order oligomeric states including dodecamers that modulate substrate specificity and degradation rates[31]. LONP2 likely assembles into similar ring structures with properties that can be regulated through oligomerization state. The concentration of LONP2 within the highly oxidizing peroxisomal crystalline core, where substrate proteins bearing hydrophobic residues characteristic of oxidative damage are most prevalent, represents an elegant evolutionary optimization positioning the protease where it is most needed.

Conclusion and Future Directions

LONP2 represents a multifunctional ATP-dependent serine protease specialized for maintaining proteostasis in the peroxisomal matrix through selective degradation of oxidatively damaged and misfolded proteins and through ATP-independent chaperone activity[4][10][12]. Localized to the peroxisomal matrix and concentrated within the oxidizing crystalline core, LONP2 functions at the interface of peroxisomal fatty acid metabolism, redox homeostasis, and protein quality control[2][7][11][30]. Through its degradation of substrates including TYSND1, catalase, and other oxidatively damaged proteins, LONP2 maintains the functional capacity of peroxisomal metabolic pathways and prevents accumulation of protein aggregates that would compromise organellar and cellular function[7][18][30][53]. Beyond local proteolytic effects, emerging evidence demonstrates that LONP2 activity dynamically regulates multiple cellular processes including lipid metabolism, stress response pathways, and ribosomal biogenesis in a cell-type-dependent manner[20][25][36].

The disease associations of LONP2 dysregulation spanning the neurodevelopmental Buratti-Harel Syndrome, cancer-associated overexpression in cervical carcinogenesis, and the emerging role of circRNA-LONP2 in cardiovascular disease underscore the critical importance of proper LONP2 regulation to cellular and organismal health[8][26][38]. Future research elucidating the precise ATP utilization mechanism of LONP2, identifying the complete repertoire of LONP2 substrates and substrate recognition determinants, investigating the dynamic regulation of protease versus chaperone activity, and exploring the integration of LONP2 function with mitochondrial quality control and organellar cross-communication will significantly advance understanding of peroxisomal biology and provide insights into disease pathogenesis. Additionally, determining whether LONP2 can be therapeutically targeted in cancer and cardiovascular disease contexts while maintaining normal developmental and metabolic functions represents an important translational avenue warranting investigation.

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42. cellular requirements[28]